The present invention relates to the field of AC electrical power supply circuits, and more particularly to AC electrical power supply circuits in which the load characteristics may be non-symmetrical.
Electrical load symmetry is defined as the impedance of the load being substantially equal whether the supplied electrical drive power is positive or negative. Symmetry is typically desired as it maintains optimum system performance.
In certain cases, for example a discharge lamp, although the basic configuration is designed in a symmetrical fashion, it may perform asymmetrically. For example, a lamp that operates with symmetric impedance when oriented horizontally may not operate symmetrically when in a vertical orientation. The voltage drop across the lamp will be different on the positive part of the cycle than on the negative part. Evaluation and possible correction of this condition can be achieved if a means is available to first detect the lack of symmetry.
Therefore, it is an object of the present invention to provide a modified AC electrical power supply drive circuit that includes means to determine the symmetry or lack thereof in a load.
This and other objects will become more apparent from the description of the invention to follow.
A circuit and method are provided for detecting an asymmetrical load characteristic when being supplied with a high frequency AC power source. The voltage across a DC blocking capacitor is compared through an operative amplifier with a scaled version of the input voltage, and any difference is signaled. The DC blocking voltage and the scaled input voltage are each further scaled down, for example to 10 percent, in order to reduce the voltages being compared, while keeping them proportional to their respective full values. Preferably, first and second connective means comprising first and second resistive dividing networks provide the scaled input voltage and the scaled DC blocking voltage, respectively.